The present invention is an improvement to the central tire inflation systems (CTIS) shown in U.S. Pat. No. 4,640,331, assigned to the Assignee of this invention, also known as onboard inflation systems and tire traction systems, wherein the inflation pressure of one or more vehicle tires may be controlled from a remote location (usually the vehicle cab) with the vehicle at rest and/or in motion and utilizing an onboard source of pressurized fluid (usually compressed air from the vehicle air brake compressor and/or a compressed air reservoir and an air circuit connecting the source to each tire).
Central tire inflation systems, also known as tire traction systems, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 2,634,782; 2,976,906; 2,989,999; 3,099,309; 3,102,573; 3,276,502; 3,276,503; 4,313,483; 4,418,737, 4,421,151 and 4,434,833, the disclosures of all of which are hereby incorporated by reference. CTIS allow the operator to remotely manually and/or automatically vary and/or maintain the inflation pressure of one or more of the vehicle tires from the vehicle (usually a truck) air system, usually while the vehicle is in motion as well as when the vehicle is at rest.
It is well known that the traction of vehicles on relatively soft terrain (i.e. on mud, sand or snow) may be greatly improved by decreasing the inflation pressure within the tires. By decreasing the inflation pressure, the tire supporting surface (usually called the "footprint") will increase thereby enlarging the contact area between the tires and the terrain. Additionally, it is often desireable to decrease the tire pressure from the over-the-road or highway inflation pressure to increase riding comfort on rough roads. On the other hand, higher tire pressures decrease rolling resistance and tire carcass temperatures on smooth roads thereby increasing economy and safety. Accordingly, in cross country vehicles it is desirable to change the inflation pressure in the pneumatic tires to fit the terrain and is also desirable that a system be provided for changing the inflation pressure of the tires from an onboard source, while the vehicle is at motion or at rest, and that the system be controlled from the vehicles operating cab. This is especially true for military vehicles which usually travel in columns whereby stoppage of the vehicle would delay the entire column. Additionally, if the military is under enemy attack, it is imperative that the vehicle maintain its maneuverability as long as is possible. If a tire has been punctured by gun fire or the like, it is imperative to be able to at least partially inflate the damaged tire, if possible, so that the vehicle remains mobile.
CTIS known in the prior art provide for isolation of a vehicle tire subject to extreme damage. However, they do not provide a means for preselecting a "run flat" mode for the CTIS whereby the controller causes system pressure to be rapidly and frequently sensed so that a tire damaged in combat, or the like, may be identified and supplied with pressurized air immediately after being damaged and whereby the compressed air stored in the undamaged vehicle tires and the vehicle compressed air reservoirs, such as the brake system, can be utilized to supplement air to a tire damaged or punctured by gunfire or the like.
U.S. Pat. No. 4,640,331, assigned to the Assignee of this invention, discloses a CTIS utilizing a valve assembly comprising a control valve and a low tire pressure shutoff valve at each wheel end assembly (usually a single or dual tire) which valve assembly is connected to the central control system by a single pressure line or conduit through a rotary seal assembly. Pressurization of the single pressure conduit is effective to open and close communication to the vehicle tire and to cause inflation and/or deflation of said tire to a selected pressure. The low tire pressure shutoff valve is effective to automatically isolate the tire associated therewith from the remainder of the central tire inflation system when the inflation pressure thereof is below a predetermined minimum reference value. However, the system pressure is measured at an infrequent rate and is unable to immediately identifying a tire damaged by gunfire, or the like, nor automatically maintain sufficient pressure therein as long as the leakage rate in the damaged tire exceeds a predetermined minimum, at which time the damaged tire is automatically isolated.
Accordingly, it is an object of the present invention to provide a new and improved central tire inflation system provided with a means for preselecting a "run flat" mode of operation enabling the system pressure to be frequently sensed so that a tire damaged in combat, or otherwise may be immediately identified and supplied with sufficient pressurized air to delay or avoid the damaged tire from being isolated.
This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiments taken in connection with the attached drawings.